Didn't see anyone answer this yet...
I managed FP+ for 10 people across 3 families and I thought I'd share some of my experience related to your question.
- As mentioned previously, you have to send and accept invitations for those you want to manage. Before doing that for all members of your party, you have to do that for those that have the MDE accounts and are managing their own families, e.g. I sent and received invitations to my dad and brother, who were managing the others in their party, and then I sent invitations for those family members that they were managing.
- One issue we encountered was with me trying to manage my mother, who was on my dad's account. After doing all of the same things I did with my brother's family, who I had no issues with, plus trying some other things, we couldn't get my mom to show up in my family/friends list.
- I called and talked to someone in the MDE technical side and was initially told that there was nothing they could do - it was just a glitch that happened sometimes.
- After thinking on this some more and realizing it could be difficult to manage 9 people's FP+ together and then 1 separately, especially if we wanted to change anything in the park on the fly, I called back and talked to a different technical rep the next day.
- She ended up telling me that this issue was the bane of her existence. Ultimately she said that this issue was caused by my dad sending an invitation to my mom with the "Invite to Plan and Share" link that appears next to her name on his family/friends page) but it basically going nowhere because she doesn't have a Disney.com account. ***Word of warning - don't do that. The rep said that the invitation just sits out there, but it also ties up all of their other entitlements, reservations, etc. The site doesnt tell you this could happen, and apparently it happens quite frequently since the language on the page make it sounds like something you should/could do (like my dad did) and based on the rep's responses to me.
- Ultimately, she was able to fix the issue using the email address my dad used for my mom, deleting the invitation to her, and then linking her to me. She didn't need any reservation numbers or anything, just email addresses used by all parties.
That's a long answer to your question, but the point is that the family/friends lists and invitations can be corrected.
Also, while talking to this same rep as she helped me clean up some of our FP+ items, I casually mentioned that the HS options were disappointing because I couldn't select Toy Story and Rock 'n' Roller Coaster. She graciously offered up to add RnRC as an extra FP+ for our party. I hesitated even mentioning that on this board because of the hassle it might cause future reps if everyone called in to ask for the same. However, in the spirit of sharing, it shows that it can be done (I now have 4 FP+ for our HS day), and it pays to be very nice and personable to Disney (really most) phone reps.
